Of the many components of cognition affected in Alzheimer's disease (AD), two particular cognitive domains have special clinical relevance: tests of episodic memory (delayed recall and recognition) are highly sensitive for detecting AD, and tests of semantic retrieval (naming and fluency) are best for staging the disease and tracking its progression. Documenting the anatomical and physiological correlates of these impairments in the living subject gives insights into the distribution of the underlying anatomical and functional brain lesions that produce AD. To pursue this approach, and thereby extend understanding of brain-behavior relations in aging and AD, the investigators propose to conduct a series of experiments over 3 years relating cognitive test performance in these two domains to hippocampal volume and to patterns of neural activation measured with functional magnetic resonance imaging.